I. Field of the Invention
The present invention generally relates to methods and apparatus for permitting periodic introduction of cleaning agents, e.g., chemical foams, into a steam turbine to remove deposits without altering the turbine system or mechanisms. More specifically, the present invention is directed to apparatus that can be attached to the steam chest of a turbine and through which foamed cleaning agents can be directly injected into the steam chest and directed to all portions of the turbine for cleaning purposes. More specifically, the present invention relates to apparatus and methods which achieve the foregoing goal while being free of moving parts after installation.
II. Description of the Background
The demand for electricity continues to expand, both within the United States and abroad. A particularly favored means for producing electricity employs steam driven turbines. As electrical demand has grown, both the number of operating turbines and their hours of operation have increased. At the same time, the need to control operating costs and to minimize environmental impact have grown. Accordingly, it is desirable that these turbines operate in the most cost and energy efficient ways possible.
Older turbines are often refurbished with newer components to improve efficiency. Replaced components may include items such as nozzle blocks and reaction blading and may, because of improved manufacturing techniques and use of harder materials, result in closer tolerances. Thus, steam flow is often restricted after refurbishment. Because these harder materials do not erode as rapidly as did the older materials, keeping the flow path clean becomes essential to maintaining efficient turbine operation. In older systems, the enlargement of the flow path cross-section caused by the erosion characteristic of older materials would, in many cases, compensate for the reduction in flow path cross-section resulting from chemicals deposited during operation. These deposits primarily comprise metals. While copper, iron and their oxides comprise the primary deposits, calcium and other chemicals are also deposited. Adequate steam flow cross-section was often maintained in older systems by the tradeoff of erosion with the growth of metallic deposits. With the harder materials characteristic of newer systems, erosion is no longer able to compensate for growth of these metallic deposits. Accordingly, both the use of harder materials and closer tolerances, together with the desire to improve operating efficiency, have all combined to create conditions more sensitive to chemical deposit and to require more frequent and better cleaning.
When metallic deposits do build up inside the turbine, it is important to remove them as quickly as possible. One approach often used has been to blast the deposits off the internal parts using grit or sand. Obviously, however, sandblasting methods require that the high pressure turbine be disassembled. The resulting costs of disassembly, cleaning, reassembly and loss of revenue during the long down times associated with sandblasting can be quite high. For example, in 1999, the typical cost for disassembly, sandblasting and reassembly of a high pressure, 350 megawatt turbine has been estimated to be about four hundred thousand dollars ($400,000.00). More importantly, at an average cost of $30/megawatt/hour for replacement power, the cost for replacing lost power would exceed two hundred fifty thousand dollars ($250,000.00) per day. Thus, sandblasting methods are avoided, if at all possible.
A much more cost effective method for removing metallic deposits has been chemical cleaning of the turbine and its internal parts. In chemical cleaning methods, foamed cleaning materials have been injected into the steam path of the turbine. The best cleaning results have been obtained by injection of foamed chemical cleaning agents with the turbine turning. Chemical cleaning methods have been successfully used by utility companies to remove metallic deposits with minimal disruption so that load losses caused by deposits in the steam paths of power turbines can be minimized.
However, chemical cleaning of a high pressure turbine requires the chemical cleaning agents, most often foamed cleaning materials, to be injected into the main steam system and to follow the steam path during normal operation. Injection ports leading into the main steam loop that feed steam to the governor or control valve system are thus required. Accordingly, it was necessary to penetrate the main steam lines to install these injection ports. The initial cost for installation of an injection port typically exceeds fifty thousand dollars ($50,000.00). Further, these installations required welding and appropriate stress relief measures, followed by testing for quality, integrity and stress, e.g., x-ray testing, prior to use. In the event that the structural integrity of the pressure vessel was effected, further repairs were then required.
After completion of the cleaning operation, the injection port must be capped, requiring additional welding and structural integrity testing before the turbine can be placed back into operation. While future cleaning could employ the same injection port, without again incurring the initial installation costs, time and expense in removing and replacing the cap and in retesting the structural integrity were not insignificant. In 1999, the estimated cost for each successive cleaning of a 350 megawatt turbine was about fifty thousand dollars ($50,000.00), not including load curtailment costs exceeding two hundred fifty thousand dollars ($250,000.00) per day to cover replacement power. Thus, while these chemical cleaning methods are more efficient and cost effective than sandblasting, they still suffer from high costs and potential safety problems.
Many of the problems associated with the cleaning methods described above were solved by the steam injection apparatus described in my prior U.S. Pat. No. 5,018,355. The injection apparatus of the '355 patent was designed to replace an existing governor or control valve on the steam chest of a high pressure turbine. Using my injector, chemical foam for cleaning metallic deposits from the interior surfaces of the turbine could be injected from outside the turbine without requiring independent penetration of the main steam loop of the turbine. When the cleaning process was finished, the original governor or control valve could be easily re-installed in a short period of time. Thus, the initial installation costs, together with the expensive and time consuming testing for structural integrity, could be eliminated because the injection apparatus employed an existing port on the steam chest. However, the reciprocating assembly of my prior injection apparatus was found to be unnecessarily complicated and, thus, suffered from potential operating problems. While my prior injection apparatus was a significant improvement over other systems, the industry has continued to seek improved, less complicated chemical injectors.
Thus, there has been a long felt but unfulfilled need for simpler, less expensive methods and apparatus for cleaning high pressure turbines. The present invention solves those needs by providing an apparatus which is capable of injecting chemical cleaning agents into the steam chest of a high pressure turbine through an existing port and which is free of moving parts after installation.